An extrusion die for extruding thin plastic films has an orifice that extends along the length of the die. In operation, molten polymer flows under pressure through an internal flow passage in the die and leaves the die via the orifice. To control the width of the thin plastic film produced using the extrusion die, for example to make wider or narrower plastic film sheets, the extrusion die includes a deckle system. When used, the deckle system is inserted into the internal flow passage of the die to prevent extrudate from flowing through that portion of the die occupied by the deckle system. In this manner, the deckle system adjusts the width of the die orifice through which molten polymer can flow and, correspondingly, the width of the extruded plastic film produced using the die.
Deckle systems for extrusion dies can have a variety of configurations. The deckles on an extrusion die may be internal to the die, external to the die, or both internal and external to the die. Internal deckles typically include one or more internal deckle members referred to as a deckle quill, flag or plug, and a deckle rod. For example, an internal deckle may include an upper deckle member referred to as a quill, a lower deckle member referred to as a flag or plug, and a deckle rod positioned below the lower deckle member. The different internal deckle components function to fill different sections of the internal flow passage of the extrusion die. For instance, the deckle rod is typically positioned in a transition zone of the extrusion die to block that portion of the internal passage of the die. The transition zone is generally the location where the internal passage narrows down to the orifice.
A problem encountered in extrusion dies with internal deckles is the lack of adequate sealing contact between the deckle rod and the internal walls of the die. A deckle rod may not adequately seal the internal passage due to manufacturing tolerances, thermal expansion of the components, wear of the components, or other issues. This may result in molten polymer leaking out of regions where the deckle rod is not in sealing contact near an end region of the die orifice. When this occurs, molten polymer can build up in the end region of the die, creating an extruded film of non-uniform width and thickness. Further, polymer accumulation can prevent movement of components of the deckle system, leading to increased replacement and maintenance costs.